System and method for enabling a high torque/high speed brushless DC motor

ABSTRACT

A high torque/high speed brushless DC motor system for controlling both the speed and torque of the motor including a rotor and a stator, the stator of the motor including a first, second and third winding. The system further includes means for sensing the position of the rotor and means for selectively configuring the first, second and third windings of the stator in a wye connection when the speed of the motor is less than a predetermined value and configuring the windings in a delta connection when the speed of the motor is greater than the predetermined value.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a brushless DC motor, and moreparticularly, to a system and method for controlling the torque andspeed of the brushless motor.

[0003] 2. Description of the Prior Art

[0004] A typical brushless DC motor includes a stator, including threewindings, spaced at 120 degree electrical from one another, forimparting a torque on a rotor. The torque imparted on the rotor causesthe rotor to rotate. Those skilled in the art of motors and generatorsappreciate the efficiency, economy and simplicity of brushless DC motorswherein there is no actual physical contact between the stator windingsand the rotor. In order to effectuate the operation of the motor, aproperly timed and spaced magnetic field is synthesized in the statorwindings which imparts a torque on the rotor and causes the rotor torotate.

[0005] The typical brushless DC motor is permanently configured in oneof two basic configurations—either a wye connection or a deltaconnection. A motor with windings configured in the delta configurationcan operate at a greater speed than the same windings configured in thewye configuration. However, a motor with windings configured in the wyeconfiguration can operate with a greater torque at low speeds than thesame windings configured in the delta configuration.

[0006] Accordingly, in an application requiring high torque at a lowspeed, the motor is permanently configured in the wye configuration.Consequently, a conventional brushless motor design requires acompromise between high torque at a low speed and low torque at a highspeed.

[0007] One application of a brushless DC motor is that of providing asource of motive energy for driving a centrifuge rotor in a centrifugesystem. A centrifuge system is a device by which liquid samples may besubjected to centrifugal forces. The sample is carried within thecentrifuge rotor, which is mounted to a rotatable drive shaft that isdriven by the brushless motor. A centrifuge system using a brushlessmotor with windings permanently configured in either a deltaconfiguration or a wye configuration is limited by the aforementionedcompromise between high torque at a low speed and low torque at a highspeed.

[0008] There is a need for a system and method for enabling a brushlessDC motor to operate with high torque at a low speed for high torque-lowspeed centrifuge rotors as well as to operate at high speeds at areduced torque for high speed-low torque centrifuge rotors, thuspermitting the use of a wide range of centrifuge rotors.

SUMMARY OF THE INVENTION

[0009] A high torque/high speed brushless DC motor system forcontrolling both the speed and torque of the motor includes a rotor anda stator. The stator of the motor includes a first, second and thirdwinding. The system further includes means for configuring the first,second and third windings in a wye connection when the speed of themotor is less than a predetermined value and configuring the windings ina delta connection when the speed of the motor is greater than thepredetermined value.

[0010] In one aspect of the invention, switching means are included inthe motor system for implementing the stator winding connectionconfiguration changes. The switching means of the system can be commonto both the wye and delta connection configurations.

[0011] A method is also disclosed herein for effectuating theconfiguration of the brushless DC motor in a wye connection when thespeed of the motor is less than the predetermined value and configuringthe windings in a delta connection when the speed of the motor is abovethe predetermined value. The method of the present invention can befurther implemented by a storage media containing computer readableprogram instructions for controlling a processor to control a brushlessDC motor in accordance with the methods of the present invention.

[0012] It yet another aspect of the invention, a storage media havingcomputer readable program instructions embodied therein for controllinga processor, which in turn, controls a brushless DC motor in accordancewith the method of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1a is a schematic diagram of a brushless DC motor systemembodying the present invention, including a stator configured in a wyeconnection;

[0014]FIG. 1b depicts the schematic diagram of the stator of FIG. 1aconfigured in a delta connection;

[0015]FIG. 2 is a schematic diagram including switching means and thewindings configured in a wye connection of the invention of FIG. 1;

[0016]FIG. 3 is a schematic diagram including switching means and thewindings configured in a delta connection of the invention of FIG. 1;and

[0017]FIG. 4 is a logical flow diagram illustrating a method of theinvention of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0018] Referring to FIG. 1a, a brushless DC motor system 1 has a rotor 5and a stator 3, the configuration of stator 3 is controlled to enablestator 3 to be selectively configured in either a wye connection or adelta connection to achieve a high motor torque, and a high speedoperation. Accordingly, a stator connection configuration procedure isused to configure stator 3 connection depending on the speed of rotor 5.

[0019] Stator 3 includes three windings, namely a first winding 52, asecond winding 54 and a third winding 56. Stator 3 is shown configuredin a wye connection in FIG. 1a and in a delta connection in FIG. 1b.Whether the stator windings are configured in a wye connection or adelta connection depends on the speed of rotor 5. To achieve a hightorque, the stator windings are configured in the wye connection shownin FIG. 1a. In order to achieve a high speed, the stator windings areconfigured in the delta connection shown in FIG. 1b. The capability tochange the configuration of the stator windings of the present inventionenables the present invention to overcome traditional maximum torque andmaximum speed limits encountered in conventional brushless DC motorsoperating with stator windings permanently configured in either a fixedwye connection or a fixed delta connection.

[0020] The brushless DC motor system 1 synthesizes a rotating magneticfield in stator 3 windings to induce a rotation of rotor 5, and inparticular, a rotation of rotor shaft 15. System 1 uses rotor positionsensors 24, 26, 28, 30, 32, and 34 to sense a position of rotor 5 forsynthesizing a rotating magnetic field in the stator 3 that is atquadrature (i.e., 90 degrees electrical) for all positions of rotor 5 toinduce a rotation of rotor shaft 15. Accordingly, the current flowthrough each of stator windings 52, 54, and 56 is sequentially switchedwith the proper timing to synthesize a rotating magnetic field in thewindings.

[0021] Referring to FIG. 1a, stator 3 has a first winding 52, a secondwinding 54 and a third winding 56. Each of the windings has a firstterminal attached to a drive signal source of a drive controller 44. Thefirst winding 52 has a first terminal attached to a drive signal source45 by the line 46, see both FIG. 1a and 1 b. The second winding 54 has afirst terminal attached to a drive signal source 47 by the line 48.Third winding 56 has a first terminal attached to a drive signal source49 by line 50.

[0022] Stator windings 52, 54, 56 are configured in the wye connectionin FIG. 1a, thus the second terminal of each of windings is connected toa common point 58. Configured in the delta connection in FIG. 1b, thesecond terminal of each winding is connected to another drive signalsource. The second terminal of first winding 52 is connected to seconddrive signal source 47 by line 48. The second terminal of second winding54 is connected to third drive signal source 49 by line 50. The secondterminal of third winding 56 is connected to first drive signal source45 by line 46.

[0023] Rotor 5 of the system 1 has four permanent magnets constitutingfour main poles 10. Rotor 5 also has a rotatable shaft 15 to which acommutation magnet 20 is attached. Commutation magnet 20 has the samenumber of magnetic poles, four, as rotor 5. Brushless DC motor system 1has rotor position sensors 24, 26, 28, 30, 32, and 34 to detect themagnetic field (i.e., the flux) originating from commutation magnet 20.System 1 typically has one rotor position sensor for each statorwinding, for each stator configuration. Thus, system 1 has six rotorposition sensors, a set of three rotor position sensors 24, 26 and 28,one for each of the stator windings, for the wye configuration; and aset of three rotor position sensors 30, 32 and 34, one for each of thestator windings, for the delta configuration. The rotor positionsensors, in one aspect of the invention, are Hall type magnetic sensors.The rotor position sensors are not limited to being Hall type sensors.

[0024] In order to synthesize a properly timed and sequenced rotatingmagnetic field, the wye rotor position sensors and delta rotor positionsensors 30, 32, 34 are separated one from the other by 120 degreeselectrical. Thus, the signals detected by adjacent wye (24, 26, 28) ordelta (30, 32, 34) sensors lag or lead one another by 120 degrees,depending on the direction of the rotor rotation. Furthermore, the threewye connection rotor position sensors 24, 26, 28 are spaced 30 degreeselectrical from the three delta connection rotor position sensors 30,32, 34. Thus, there is a 30 degree difference between correspondingdetected wye and delta sensor signals.

[0025] The magnetic flux originating in commutation magnet 20 anddetected by rotor position sensors 24, 26, 28, 30, 32 and 34 generate athree phase encoded signal. The phase encoded signal is provided to adrive controller 44 by lines 38 and 40. Drive controller 44 includes adecoder that interprets the phase-encoded signal so that the drivecontroller can switch the current flow through the stator windings offand on in the proper sequence and with the proper timing to produce arotating magnetic field in stator 3 that induces a rotation ofcommutation magnet 20, and thus rotor 5.

[0026] Although a total of six rotor position sensors are depicted inFIG. 1a, three each for the wye configuration and the deltaconfiguration of the stator windings, brushless DC motor system 1 mayinstead have only three rotor position sensors. The single set of threerotor position sensors detect the position of the rotor 5 when the rotorwindings are configured in both a wye connection and a delta connection.Due to the aforementioned 30 degree phase difference between the wye anddelta rotor position sensors and the three phase encoded signalsdetected by the same, a microprocessor or other means, is used at thetransition between wye and delta stator configuration to shift thesignal sensed by the rotor position sensors by 30 degrees when usingonly one set of three rotor position sensors. The phase shift accountsfor 30 degree phase shift of line to line voltages when the windings areswitched from the wye to the delta configuration.

[0027] As indicated above, the brushless DC motor system 1 is enabled tobe configured with the stator windings in a wye connection so that themotor can achieve high torque operation. Referring to FIG. 2, aschematic of drive controller 44, the windings and a switching means 65with the windings configured in the wye connection is shown. As FIG. 2shows, the first terminal of windings 52, 54 and 56 have a firstterminal connected to the first, second and third drive signal sources45, 47 and 49, respectively. The second terminal of the first, secondand third windings are connected to points 60, 62 and 64 which are alltied together(i.e., common) in the switching means 65.

[0028] The FIG. 3 shows a schematic of drive controller 44, the windingsand switching means 65 with the windings configured in the deltaconnection. The first terminal of each of the three windings 52, 54 and56 has a first terminal connected to the first, second and third drivesignal sources 45, 47 and 49, respectively. The second terminal of firstwinding 52 is connected to second drive signal source 47 by line 48; thesecond terminal of second winding 54 is connected to third drive signalsource 49 by line 50; and the second terminal of third winding 56 isconnected to first drive signal source 45 by line 46.

[0029] The FIGS. 2 and 3 depict the substantially the same components,the difference is that switching means 65 is configured to selectivelyconnect stator windings 52, 54, 56 in the wye connection in FIG. 2 andthe switching means 65 is configured to selectively connect statorwindings 52, 54, 56 in the delta connection in FIG. 3. Common to eachconfiguration however, there is a switching signal that is sent from thedrive controller 44 to switching means 65 by line 59. The switchingsignal enables control of switching means 65 to change the configurationof the windings from the wye connection to delta connection and viceversa. The phase encoded signals, containing information related to therelative position of rotor 5, from rotor position sensors 24, 26, 28,30, 32 and 34 are supplied to drive controller 44 by line 39.

[0030] Referring to the logical flow diagram of FIG. 4, the inventionwill be further described. The stator windings 52, 54, 56 of thebrushless DC motor system 1 are first configured in a wye connection(step 100). This is the typical starting configuration since the statorwindings 52, 54, 56 are configured in the wye connection for low speeds(and high torque). To enable the proper timing of the rotating magneticfield in the stator required to initiate and sustain rotation of therotor, the wye connection rotor position sensors 24, 26, 28 areconnected to the drive controller (step 105). The motor is acceleratedby synthesizing a rotating magnetic field in the stator windings 52, 54,56 (step 110). A determination is then made whether the motor hasreached a selected, predetermined threshold speed (step 115). Thethreshold speed is the predetermined speed above which the configurationof the motor is switched from the wye connection to the delta connectionso that high speed (and low torque) operation of the motor can beachieved. When the speed is determined to be below the threshold speed,the speed of the motor is recursively checked (steps 115, 120 and 110)until the threshold speed is exceeded (step 115) or the desired targetspeed is obtained (step 120). Thereafter, the configuration process isended since there is no longer a need to accelerate the motor, and thespeed of the motor is maintained at the target speed.

[0031] When a determination is made at step 115 that the threshold speedhas been exceeded, then a determination is made whether the windings 52,54, 56 are already configured in the delta connection (step 123). If thewindings 52, 54, 56 are configured in the delta connection, then thespeed of the motor is checked to determine whether the motor has reachedits target speed (step 120). If the windings 52, 54, 56 of the motor arenot configured delta configuration, then the motor enters a momentarydrive coast (step 125). Next, the windings 52, 54, 56 are configured forthe delta connection (step 130) and the rotor position sensors for thedelta configuration 30, 32, 34 are connected (step 135). Thereafter, theconfiguration process continues with the continued acceleration,verification and/or maintenance (steps 110, 115 and 120) of the motorspeed until the target speed is obtained.

[0032] Those skilled in the art, having the benefit of the teachings ofthe present invention may impart numerous modifications thereto withoutdeparting from the present invention. Such modifications, such as, forexample, including computer readable program instructions embodied on astorage media such as a CD-ROM or other static memory, for carrying outthe methods of the present invention are to be construed as lying withinthe scope of the present invention, as defined by the appended claims.

What is claimed is:
 1. A method for controlling a brushless DC motor,said motor including a rotor and a stator, said stator comprising afirst winding, a second winding and a third winding, said methodcomprising the steps of: (a) configuring said first, second and thirdwindings in a wye connection when the speed of said motor is less than apredetermined value; and (b) configuring said first, second and thirdwindings in a delta connection when the speed of said motor is greaterthan said predetermined value.
 2. The method of claim 1, wherein step(a) comprises: controlling a first switch means to connect a firstterminal of said first winding to a first drive signal source and asecond terminal of said first winding to a common node; controlling asecond switch means to connect a first terminal of said second windingto a second drive signal source and a second terminal of said secondwinding to said common node; and controlling a third switch means toconnect a first terminal of said third winding to a third drive signalsource and a second terminal of said third winding to said common node.3. The method of claim 1, wherein step (b) comprises: controlling afirst switch means to connect a first terminal of said first winding toa first drive signal source and a second terminal of said first windingto a second drive signal source; controlling a second switch means toconnect a first terminal of said second winding to said second drivesignal source and a second terminal of said second winding to a thirddrive signal source; and controlling a third switch means to connect afirst terminal of said third winding to said third drive signal sourceand a second terminal of said third winding to said first drive signalsource.
 4. The method of claim 1, wherein said first winding has a firstterminal connected to a first drive signal source, said second windinghas a first terminal connected to a second drive signal source, saidthird winding has a first terminal connected to a third drive signalsource, and wherein step (a) comprises: controlling a first switch meansfor connecting a second terminal of said first winding to a common node;controlling a second switch means for connecting a second terminal ofsaid second winding to said common node; and controlling a third switchmeans for connecting a second terminal of said third winding to saidcommon node; and wherein step (b) comprises: controlling said firstswitch means for connecting said second terminal of said first windingto said second drive signal source; controlling said second switch meansfor connecting said second terminal of said second winding to said thirddrive signal; and controlling said third switch means for connectingsaid second terminal of said third winding to said first drive signalsource.
 5. The method of claim 1 wherein step (a) further comprises:sensing a position of said rotor using a first set of rotor positionsensors, one rotor position sensor for each of said windings; andsynthesizing a rotating magnetic field in said windings by sequentiallyswitching a current flow through said windings in response to said rotorposition sensed by said first set of rotor position sensors; and step(b) further comprises: sensing said position of said rotor using asecond set of rotor position sensors, one rotor position sensor for eachof said windings; and synthesizing a rotating magnetic field in saidwindings by sequentially switching said current flow through saidwindings in response to said rotor position sensed by said second set ofrotor position sensors.
 6. The method of claim 5 wherein said rotorposition sensors comprise Hall type magnetic sensors.
 7. The method ofclaim 1 wherein step (a) further comprises: sensing a position of saidrotor using a set of rotor position sensors, one rotor position sensorfor each of said windings; and synthesizing a rotating magnetic field insaid windings by sequentially switching a current flow through saidwindings in response to said rotor position sensed by said rotorposition sensors; and step (b) further comprises: sensing said positionof said rotor using said rotor position sensors; and synthesizing arotating magnetic field in said windings by sequentially switching saidcurrent flow through said windings in response to said rotor positionsensed by said rotor position sensors, wherein the phase of said rotorposition sensors in step(a) and step (b) differs by a phase shift. 8.The method of claim 7 wherein the phase of said rotor position sensorsin step (a) and step (b) differs by a phase shift of about thirtydegrees electrical.
 9. The method of claim 7 wherein said rotor positionsensors comprise Hall type magnetic sensors.
 10. The method of claim 7wherein a processor controls the phase shifting of said rotor positionsensors.
 11. The method of claim 1 wherein the torque of said motor ishigher at speeds lower than said predetermined value than at speedsgreater than said predetermined value.
 12. A system for controlling abrushless DC motor, said motor including a rotor and a stator, saidstator including a first winding, a second winding and a third winding,said system comprising: means for selectively configuring said first,second and third windings in a wye connection when the speed of saidmotor is less than a predetermined value, and for selectivelyconfiguring said first, second and third windings in a delta connectionwhen the speed of said motor is greater than said predetermined value.13. The system of claim 12 wherein, for said wye connection, saidconfiguring means comprises: a first switch means for connecting a firstterminal of said first winding to a first drive signal source and asecond terminal of said first winding to a common node; a second switchmeans for connecting a first terminal of said second winding to a seconddrive signal source and a second terminal of said second winding to saidcommon node; and a third switch means for connecting a first terminal ofsaid third winding to a third drive signal source and a second terminalof said third winding to said common node.
 14. The system of claim 12wherein, for said delta connection, said configuring means comprises: afirst switch means for connecting a first terminal of said first windingto a first drive signal source and a second terminal of said firstwinding to a second drive signal source; a second switch means forconnecting a first terminal of said second winding to said second drivesignal source and a second terminal of said second winding to a thirddrive signal source; and a third switch means for connecting a firstterminal of said third winding to said third drive signal source and asecond terminal of said third winding to said first drive signal source.15. The system of claim 12, wherein said first winding has a firstterminal connected to a first drive signal source, said second windinghas a first terminal connected to a second drive signal source, saidthird winding has a first terminal connected to a third drive signalsource, and said configuring means comprises: a first switch means forconnecting a second terminal of said first winding to a common node forsaid wye connection configuration, and for connecting said secondterminal of said first winding to said second drive signal source forsaid delta connection configuration; a second switch means forconnecting a second terminal of said second winding to said common nodefor said wye connection configuration, and for connecting said secondterminal of said second winding to said third drive signal for saiddelta connection configuration; a third switch means for connecting asecond terminal of said third winding to said common node for said wyeconnection configuration, and for connecting said second terminal ofsaid third winding to said first drive signal source for said deltaconnection configuration; and a processor for controlling said first,second and third switch means.
 16. The system of claim 12 wherein saidconfiguring means further comprises: a first set of rotor positionsensors for sensing a position of said rotor for said wye connectionconfiguration, one rotor position sensor for each of said windings;means for synthesizing a rotating magnetic field in said windings forsaid wye connection configuration by sequentially switching a currentflow through said windings in response to said rotor position sensed bysaid first set of rotor position sensors; a second set of rotor positionsensors for sensing said position of said rotor for said deltaconnection configuration, one rotor position sensor for each of saidwindings; and means for synthesizing a rotating magnetic field in saidwindings for said delta connection configuration by sequentiallyswitching said current flow through said windings in response to saidrotor position sensed by said second set of rotor position sensors. 17.The system of claim 16 wherein said first set of rotor position sensorsand said second set of rotor position sensors differ in phase.
 18. Thesystem of claim 17 wherein said first set of rotor position sensors andsaid second set of rotor position sensors differ in phase by about 30degrees electrical.
 19. The system of claim 16 wherein said rotorposition sensors comprise Hall type magnetic sensors.
 20. The system ofclaim 12 wherein said configuring means further comprises: a set ofrotor position sensors for sensing a position of said rotor, one rotorposition sensor for each of said windings; means for synthesizing arotating magnetic field in said windings for said wye connectionconfiguration by sequentially switching a current flow through saidwindings in response to said rotor position sensed by said rotorposition sensors; and means for synthesizing a rotating magnetic fieldin said windings for said delta connection configuration by sequentiallyswitching said current flow through said windings in response to saidrotor position sensed by said rotor position sensors, wherein the phaseof said set of rotor position sensors configured for said wye connectionconfiguration differs by a phase shift.
 21. The system of claim 20wherein the phase of said set of rotor position sensors configured forsaid wye connection configuration differs by a phase shift of aboutthirty degrees electrical from the phase of said set of rotor positionsensors configured for said delta connection configuration.
 22. Thesystem of claim 20 wherein said rotor position sensors comprises Halltype sensors.
 23. The system of claim 20 further comprising a processorfor controlling the phase shift of said rotor position sensors.
 24. Thesystem of claim 12 wherein the torque of said motor is higher at speedslower than said predetermined value than at speeds greater than saidpredetermined value
 25. A storage media having computer readable programinstructions embodied therein for controlling a processor, which inturn, controls a brushless DC motor, said motor including a rotor and astator, said stator including a first winding, a second winding and athird winding, said storage media comprising: (a) program instructionsfor controlling said processor to configure said first, second and thirdwindings in a wye connection when the speed of said motor is less than apredetermined value; and (b) program instructions for controlling saidprocessor to configure said first, second and third windings in a deltaconnection when said speed is greater than said predetermined value. 26.The storage media of claim 25, wherein program instructions (a)comprises: program instructions for controlling said processor tocontrol a first switch means to connect a first terminal of said firstwinding to a first drive signal source and a second terminal of saidfirst winding to a common node; program instructions for controllingsaid processor to control a second switch means to connect a firstterminal of said second winding to a second drive signal source and asecond terminal of said second winding to said common node; and programinstructions for controlling said processor to control a third switchmeans to connect a first terminal of said third winding to a third drivesignal source and a second terminal of said third winding to said commonnode.
 27. The storage media of claim 25, wherein program instructions(b) comprises: program instructions for controlling said processor tocontrol a first switch means to connect a first terminal of said firstwinding to a first drive signal source and a second terminal of saidfirst winding to a second drive signal source; program instructions forcontrolling said processor to control a second switch means to connect afirst terminal of said second winding to said second drive signal sourceand a second terminal of said second winding to a third drive signalsource; and program instructions for controlling said processor tocontrol a third switch means to connect a first terminal of said thirdwinding to said third drive signal source and a second terminal of saidthird winding to said first drive signal source.
 28. The storage mediaof claim 25, wherein said first winding has a first terminal connectedto a first drive signal source, said second winding has a first terminalconnected to a second drive signal source, said third winding has afirst terminal connected to a third drive signal source, and whereinprogram instructions (a) comprises: program instructions for controllingsaid processor to control a first switch means for connecting a secondterminal of said first winding to a common node; program instructionsfor controlling said processor to control a second switch means forconnecting a second terminal of said second winding to said common node;program instructions for controlling said processor to control a thirdswitch means for connecting a second terminal of said third winding tosaid common node; and wherein means (b) comprises: program instructionsfor controlling said processor to control said first switch means forconnecting said second terminal of said first winding to said seconddrive signal source; program instructions for controlling said processorto control said second switch means for connecting said second terminalof said second winding to said third drive signal; and programinstructions for controlling said processor to control said third switchmeans for connecting said second terminal of said third winding to saidfirst drive signal source.
 29. The storage media of claim 25 whereinmeans (a) further comprises: program instructions for controlling saidprocessor to control a first set of position sensors, one sensor foreach of said windings, for sensing a position of said rotor for said wyeconnection configuration; program instructions for controlling saidprocessor to control a sequential switching of a current flow throughsaid windings in response to said rotor position sensed by said firstset of rotor position sensors, whereby a rotating magnetic field issynthesized in said stator for said wye connection configuration; andmeans (b) further comprises: program instructions for controlling saidprocessor to control a second set of position sensors, one sensor foreach of said windings, for sensing said position of said rotor for saiddelta connection configuration; and program instructions for controllingsaid processor to control a sequential switching of said current flowthrough said windings in response to said rotor position sensed by saidsecond set of rotor position sensors, whereby a rotating magnetic fieldis synthesized in said stator for said delta connection configuration.30. The storage media of claim 29 wherein the phases of said sets ofrotor position sensors differ.
 31. The storage media of claim 30 whereinthe phases of said sets of rotor position sensors differs by aboutthirty degrees electrical.
 32. The storage media of claim 29 whereinsaid first and second position sensors controlled by said processorcomprise Hall type magnetic sensors.
 33. The storage media of claim 25wherein means (a) further comprises: program instructions forcontrolling said processor to control a set of position sensors, onesensor for each of said windings, for sensing a position of said rotorfor said wye connection configuration; program instructions forcontrolling said processor to control a sequential switching of acurrent flow through said windings in response to said rotor positionsensed by said set of rotor position sensors, whereby a rotatingmagnetic field is synthesized in said stator for said wye connectionconfiguration; and means (b) further comprises: program instructions forcontrolling said processor to control said set of position sensors, onesensor for each of said windings, for sensing a position of said rotorfor said delta connection configuration; and program instructions forcontrolling said processor to control a sequential switching of saidcurrent flow through said windings in response to said rotor positionsensed by said set of rotor position sensors, whereby a rotatingmagnetic field is synthesized in said stator for said delta connectionconfiguration and wherein the phase of said set of rotor positionsensors configured for said wye connection configuration differs by aphase shift from the phase of said set of rotor position sensorsconfigured for said delta connection configuration.
 34. The storagemedia of claim 33 wherein the phase of said set of rotor positionsensors configured for said wye connection configuration differs by aphase shift from the phase of about thirty degrees electrical from thephase of said set of rotor position sensors configured for said deltaconnection configuration.
 35. The storage media of claim 33 wherein saidset of rotor position sensors controlled by said processor comprise Halltype magnetic sensors.